The present invention is directed to fiber optical transport systems. More particularly, the invention provides a method and system for integrating semiconductor (InP) laser/modulator chips on an aluminum nitride submount with a silica/silicon AWG. Merely by way of example, the invention has been applied to a wavelength multiplexed transmitter array. But it would be recognized that the invention has a much broader range of applicability.
Since its deployment in the middle of 1990s, dense wavelength division multiplexing (DWDM) has become a dominant technology for all long haul and regional backbone transport networks, and is gradually making its way to metro area networks. As the technology is maturing, the cost for making such systems and related components has been decreasing. Now the price bottleneck is moving toward the packaging cost of each individual optical component, such as lasers, modulators, and MUX/DEMUX filters.
Currently optical components in a DWDM transport system are individually packaged. The packaging cost of these components (e.g., a 10 G transmitter) becomes a bottleneck, preventing further reduction in price. For example, the cost of a bare DFB laser chip is only a few dollars, while a packaged DFB laser sells for several hundred dollars. Thus, for a DWDM system vendor to be competitive, it is desirable to remove this price bottleneck, making the packaging cost a less concern in manufacturing optical components.
In a conventional DWDM transport system, each optical component, either a laser or a MUX filter, is individually packaged. For example, a line card is built around a transmitter/receiver module which includes a laser, a modulator (or an integrated laser/modulator) and a receiver. The laser comes typically as an InP chip sitting inside a Butterfly package. The optical output of the line card is combined with other line cards of different wavelengths via a wavelength multiplexer which often includes an arrayed waveguide grating (AWG) made of silica-on-silicon. These line cards are connected to the multiplexer card using fiber jumpers and the combined optical output is then amplified before launching into a fiber network.
Even though these conventional DWDM systems are useful in some areas, they have many limitations that restrict their effectiveness in broader applications. Some of these limitations are discussed below, and improved techniques based on embodiments of the present invention are presented.